The photopolymerization or radiation-based curing of light sensitive materials is a multibillion dollar business. The photopolymer products of these processes are typically derived from polymers, oligomers, and/or monomers that can be selectively polymerized and/or crosslinked upon imagewise exposure to various types of electromagnetic radiation, including ultra-violet light, visible light, and electron beam radiation. Significant advantages that photopolymerizable systems have over other polymerization techniques, such as traditional thermal processing methods, include low energy requirements, spatial and temporal control of initiation, solvent-free formulations, and high polymerization rates at room temperature. They also provide tremendous chemical versatility in view of the wide range of monomers that can be photochemically polymerized.
Due to this unique set of advantages, photopolymerization systems have gained prominence for the solvent-free curing of polymer films as well as emerging applications in biomedical materials, conformal coatings, electronic and optical materials, and rapid prototyping of three dimensional objects. More specifically, photopolymers are made into different forms including films, sheets, liquids, and solutions, which are utilized in, e.g., printing plates, photoresists, stereolithography, and imaging. To further illustrate, photoresists are used to fabricate integrated circuits, flat panel displays, printed circuits, screen printing products, chemically milled parts, and micro- and nano-electromechanical systems (MEMS/NEMS). Liquid compositions can also be used for non-imaging applications such as adhesives, coatings, paints, inks, and related photosensitive products. Photopolymerizations also have in vivo applications in, e.g., open environments such as the oral cavity in addition to uses in invasive and minimally invasive surgery. In vivo photopolymerizations have even been performed transdermally.
Photopolymerization systems, processes, and related applications of radiation cured polymers are further described in a variety of general reference sources. Certain of these include, e.g., Lowe et al., Test Methods for UV and EB Curable Systems, Wiley—SITA Technology (1997), Drobny, Radiation Technology for Polymers, CRC Press (2002), Datta, Rubber Curing Systems (Rapra Review Report 144), Rapra (2002), Provder et al. (Eds.), Film Formation in Coatings: Mechanisms, Properties, and Morphology (ACS Symposium Series 790), American Chemical Society (2001), Mehnert et al., Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints, Vol. 1: UV & EB Curing Technology & Equipment, Wiley—SITA Technology (1999), Neckers et al., Chemistry & Technology of UV & EB Formulation for Coatings, Inks & Paints, Vol. 7: Photoinitiation for Polymerization: UV & EB at the Millenium, Wiley—SITA Technology (1999), Satas et al. (Eds.), Coatings Technology Handbook, 2nd Ed., Marcel Dekker (2001), Bradley (ed.), Chemistry & Technology of UV & EB Formulation, Vol. 3: Photoinitators for Free Radical Cationic & Anionic Photopolymerization, 2nd Ed., Wiley—SITA Technology (1998), Warson et al., Applications of Synthetic Resin Latices, Vol. 1: Fundamental Chemistry of Latices and Applications in Adhesives, John Wiley & Sons (2001), Davidson, Radiation Curing (Rapra Review Report 136), Rapra (2001), and Fouassier, Photoinitiated Polymerisation: Theory and Applications (Rapra Review Report 100), Rapra (1997).
The quality and performance of polymers are linked to the cure characteristics of the polymerization system. Monomers that include multiple vinyl functionalities are an industry standard in many common photopolymerization schemes. Many of these multi-vinyl monomer-based polymerizations suffer from significant limitations. To illustrate, multi-vinyl monomers typically react to far less than quantitative double bond conversion. This generally results in polymeric materials having relatively high residual/leachable monomer content. Accordingly, these materials are often toxic and have limited durability. In addition to incomplete reactions, multi-vinyl monomer-based polymerizations are typically slow, requiring lengthy exposure times at high radiation intensities. These aspects increase production costs and generally have negative environmental implications.
In view of the foregoing discussion, it is apparent that there is a substantial need for monomers that have higher polymerization rates and that polymerize more completely than conventional monomers with multiple vinyl functionalities. For example, improvements in monomer curing efficiency would allow optimum polymer properties to be achieved with minimized irradiation times and intensities. These and a variety of other features of the present invention will become apparent upon complete review of the following disclosure.